1. Field of the Invention
The present invention relates to differential protection circuitry for electrical devices such as generators, busbars, line sections, etc.
2. Prior Art
Known percentage differential protection circuits may have certain difficulties in operating correctly when the characteristic of the current measuring transformers is poor, or when the current measuring transformers have difficulties in maintaining and delivering correct measurement values for a sufficiently long measuring time. In the known protecting circuits, an analogous comparison is made of the measuring quantities in the measuring circuit of the protection circuit corresponding to the primary quantities in the supervised device. Differences in properties of the current measuring transformers, therefore in some cases, make it difficult for the protection circuit to operate properly under all circumstances.